Although many of congenital lung anomalies present early in life with dramatic symptoms and physical findings, most remain occult until late childhood and even into adult life. These uncommon lesions arise from aberrations in normal aerodigestive tract development, which begins during the fourth week of fetal life when the lung bud forms at the caudal end of a groove in the primordial pharynx. An initial phase of sequential airway branching occurs until as many as 20–25 generations are reached by the 16th week of fetal life. These branches are divided into three zones: a proximal conductive zone (branches 1–16), an intermediate transitional zone (branches 17–19), and a distal respiratory zone (branches 20–25). A second canalicular phase is then entered as capillaries develop in the distal air passages.
Atresia of the tracheobronchial tree can occur at any level and may involve an isolated segment or multiple diffuse areas of the airway. Tracheal atresia is associated with polyhydramnios, prematurity, esophageal atresia, tracheoesophageal fistula. Typically, neonates present with intractable cyanosis and despite a normal-appearing larynx are unable to be intubated. Emergency tracheostomy can be life-sustaining in babies with isolated subglottic atresia; in other infants with more diffuse disease, mask ventilation can achieve some palliation through anomalous esophagobronchial connections. Diffuse airway involvement, however, is invariably fatal.
Isolated bronchial atresia results in a bronchus that ends in a blind pouch. A mucocele develops distal to the obstruction and, as a result of compression of neighboring normal bronchial structures, causes emphysematous changes in the surrounding lung. Since children frequently develop wheezing, stridor, and pulmonary infections in the involved segments, resection is almost always indicated. Like bronchial atresia, true congenital bronchial stenosis is rare, although right main stem bronchial stenosis occurs not infrequently from iatrogenic airway trauma in chronically ventilated patients.
Related anomalies of the tracheobronchial tree include anomalous tracheal or esophageal bronchi tracheal diverticula. These rare lesions often present with symptoms of bronchial obstruction and in many cases require resection of involved lung tissue due to chronic infection and the development of bronchiectasis (see below). Similar to pulmonary sequestration, these lesions can have a dominant systemic arterial blood supply that must be kept in mind if operation is contemplated.
Abnormal budding of the foregut during development can result in the formation of bronchogenic cysts. These occur most commonly in the pulmonary hilum (primarily in the paratracheal and subcarinal areas) but can also arise in the pulmonary parenchyma. The cysts are usually single, are lined by cuboidal respiratory epithelium, and occur preferentially in the lower lobes. The cyst wall is generally thin, occasionally containing cartilage, and except for mediastinal cysts they frequently communicate with the tracheobronchial tree. Radiographically, these cysts appear as discrete round densities that often are sharply defined and air-filled. They may also present as a solitary pulmonary nodule (if completely fluid-filled) or as a pulmonary abscess with an air-fluid level (see below). In general, mediastinal bronchogenic cysts present with airway compression and parenchymal cysts are manifested by pulmonary infection. Some cysts have been noted to enlarge rapidly and rupture into the pleural space, causing tension pneumothorax. All bronchogenic cysts — regardless of location —are best treated with either simple or segmental resection. Rarely, lobectomy is required.
Bronchopulmonary dysplasia includes pulmonary agenesis and aplasia as well as primary and secondary pulmonary hypoplasia. Unilateral pulmonary agenesis occurs when one lung and the associated vascular structures fail to develop. Neonates with pulmonary agenesis may present with cyanosis, particularly if associated cardiac anomalies exist (50% of cases). Some patients, however, remain asymptomatic until childhood, when they complain of dyspnea and wheezing suggestive of asthma. Physical examination in these patients reveals marked tracheal deviation toward the side of the agenesis, and chest x-ray, barium esophagography, and chest CT may be required to exclude other diagnostic possibilities such as total lung atelectasis from foreign body aspiration, total lung sequestration, and esophageal bronchus. Once bronchopulmonary dysplasia is diagnosed, treatment is limited to supportive care. The prognosis is guarded since only two-thirds of patients survive for longer than 5 years — succumbing in part from the coexisting cardiac disease. Pulmonary aplasia is essentially identical to pulmonary agenesis except that a blind bronchial tumor stump of varying length exists and can chronically soil the normal lung with infected pooled secretions. This problem necessitates resection of the bronchial stump to prevent this potentially fatal complication.
This congenital lung anomaly is an abnormally low radial alveolus count and low ratio of lung weight to body weight and is considered primary if no inciting cause can be identified. These neonates present with hypoxemia resistant to administration of supplemental oxygen due to abnormal thickening of the pulmonary arteriolar wall. Persistent fetal circulation, hypoxemia, hypercapnia, and acidosis lead to early death in over 75% of patients. Secondary pulmonary hypoplasia results from numerous fetal and maternal abnormalities that physically restrict lung growth and development. Other conditions associated with secondary pulmonary hypoplasia include those that produce oligohydramnios and direct chest compression (renal dysplasia, and amniotic fluid leaks); those with abnormal bone development and small rigid chest walls (eg, achondroplasia, chondrodystrophia fetalis calcificans, osteogenesis imperfecta, and spondyloepiphysial dysplasia); those with decreased fetal respiratory movements (eg, phrenic nerve agenesis, abdominal masses or ascites with elevation of the diaphragm, arthrogryposis multiplex congenita, camptodactyly, and congenial myotonic dystrophy); those with intrathoracic mass lesions and those with pulmonary vascular abnormalities (eg, scimitar syndrome and pulmonary artery agenesis).